Spring and autumn phenology of Bulgarian and German provenances of Common beech (Fagus sylvatica L.) under similar climatic conditions

The ongoing climate change creates serious concerns about how tree species will behave under new environmental condi­tions. Common beech (Fagus sylvatica L.), a main and important tree species in Europe, will also be affected by the coming changes. One possibility to test the adaptability of this tree species is to perform provenance tests, transplanting trees from northern areas to warmer and drier places, and to investigate their behavior over a long period of time (transfer experiments). This work describes such an experiment. A provenance test was established in April 2010 with two-year-old seedlings from 8 provenances of beech - 5 from Germany (Bavaria) and 3 from Bulgaria. Our purposes were to determine differences in the manifestation of the spring and autumn phenophases from beech of German and Bulgarian provenances and to seek a relationship between geographical coordinates and altitude of the same provenances and timing of leaf flushing and leaf coloring/shedding. In this experiment we examined leaf unfolding and leaf coloring/shedding in two growing periods (2013 and 2016). We found that the Bulgarian provenances flushed earlier in comparison with the German ones in both growing periods. No statistically significant clustering of the Bulgarian and German provenances during leaf coloring/shedding for the second period of observation was found. Longitude had the most important influence on flushing. A linear relationship between the mean date of leaf coloring and the longitude and latitude was determined, but only for the first growing period (2013), when eastern provenances had later leaf coloring, while more northern provenances had earlier leaf coloring.